Processing of cellulose fiber



@et 8, 1929. M. o. scHuR lET Al.-,

l PROCESSING OF CELLULOSE FIBER Filed Aug-l0. 1.927 2 sheets-Sneep 0.scHUR AL 1,730,387

PROCESSING OF GELLULOSE FIBER Filed Aug. 10, 19274 2 sheets-sheet `2Patented Oct. 8, 1929" UNITED STATES PATNT oFFlcE MILTON 0. SCHURAND`ROYAL H. RASCH, OF BERLIN, NEW HAMPSHIRE, ASSIGNORS TO BROWNCOMPANY, OF BERLIN, NEW HAMPSHIRE, ACORPORATION OF'MAINE PROCESSING 0FCELLULOSE FIBER Application' mea August 1o, 1927. ,smal no. 12,000.

This invention relates to a processing of cellulose liberparticularlyintended to produce a product having 'a minimum amount ofresinous impurities.

One major source .of trouble with cellulose liber used asa .raw materialfor the' production of high grade papers and derivatives.'-

lies in the resinous impurities which are likely to be presenttherein.Even though these resinous impurities are present in relatively smallamount, they impairv the color stability of paper prepared from thefiber and if 'the fiber is converted into derivatives the impurities areconverted along with the cellulose into reaction products which not onlyimpair the stability ifv the derivatives but also impart a certainamount of color thereto. The resinous matter is usually present to theextent of about 0.5% to 0.8% in bleached sulphite pulp, to the extent ofabout 0.2% to 0.4% in Wood pulp refined to high alpha cellulose content,and to about the same extent in cotton. When these impurities areremoved from the fiber, not only is its color s tability greatlyenhanced, but cellulose derivatives prepared from such fiber areimproved to an important and surprising degree, both in stability and infreedom from'color. The deresinified fiber is hence more suitable foruse as a raw material for the manufacture of paper and for theproduction of rayon and other synthetic cellulose products, where purityofthe raw material is of great moment.

In accordance with the present invention,

the resinous impurities, including resins,

gums, waxes, fats and oils, are removed from the fiberv by extractionwith organic solvents, such as alcohol, ether, chloroform, and the like.When thus extracted, the fiber becomes more stable toward heat andlight, and yields derivatives of greatly enhanced quaility. When Woodfiber, in addition to being extracted, is refined to high alphacellulose content, it yields derivatives-as stable and as free fromcoloring matter as those prepared from high grade cotton., The'vp'rocessof the present invention, Whilel applicable'to cellulose iber derivedfrom variousl sources, is hence particularly advantageous in the case ofwood liber refined to high alpha cellulose gamma celluloses, resinousmatter, and other non-alpha cellulose components 'in the pulp, so thatthe digested pulp `is of high alpha ce1- lulose content, requiringrelatively litt-le bleach to attain hi h whiteness. The resultingrefined pulp, owever, still contains residual resinous impurities whichimpair its quality. In accordance with the present invention, the pulpis subjected to extraction with an organiclsolvent at one or more stagesof the refining process to remove these impurities. It is usuallyexpedient to extract the bleached product, as it is generally run over adryer and rid of substantially all of its water content, thus becominbetter adapted for extraction. If the fiber 1s shipped in the form ofthin paper prepared for nitration, the impurities may be extracted fromsuch paper. Even the nitration rades of rag tissue may be extracted to avantage, as substantial improvement in the color of theresultingcellulose nitrateis realized.

If the fiber is handled in sheet form, it may be passed through one ormore pans containing solvent, until freed of its resin content, and thenpassed over warming rolls to remove the solvent therefrom. If thesolvent is immiscible with water, its recovery-is readilyv effected byreplacement with `water, as cellulose fiber has much greater afiinityforwater than for water-immiscible solvents such as carbon tetrachloride orether. It may, however, be more expedient to handle the fiber in theform of pulp or in the form of shredded paper, particularly when thesolvent employed is water-misci le and it is desired to eiect itsrecovery in leconomical fashion. Extraction may be effected while thefiber is being passed through and its wa-l content and intended to serveas a cotton y ter content rst displaced with solvent andl then withwater in continuous countercurrent flow apparatus. Mixed solvents, or asuc cession of two or more different solvents, one capable of removingmaterial insoluble in the other, may be advantageously employed.

On the accompanying drawings,

Figure 1 represents somewhat diagrammatically and conventionallyapparatus intended `for extracting ber in the form of a sheet.

Figure 2. is a similar representation of apparatus intended to handleber in the form of a pulp suspension or shredded paper.

Referring to Figure 1 of the drawings, 1 represents a dryer roll overwhich cellulose ber passes either in the form of a relatively thicksheet composed of unbeaten ber or in the form of thin paper or tissue.The sheet coming from the dryer roll is passed under a roll 2, servingto guide theV sheet into a bath of solvent maintained in a pan 3. Thesolvent employed, for example alcohol, is effective in extractingresinous impurities from the ber and lmay be raised in temperature toincrease the rate of extraction. The sheet is guided from the bath byaroll 4 partially submerged in the solvent and against which presses'anupper roll 5 serving to remove excess solvent from the sheet as itpasses from the bath. The sheet may then be extracted with anothersolvent, for example i carbon tetrachloride, which is capable ofextracting material which is unextractable by the rst solvent. The sheetis shown passing over a roll 6 and under a roll 7, serving to direct thepaper into a second bath of solvent in a pan 8, and thence between rolls9 and 10,

- similarto the rolls 4 and 5. If the solvent 'employed in the pan 8 isimmiscible with water, such for example as carbon tetrachloride, easyrecovery thereof may be eff fected. As shown, the sheet, after emergencefrom between the rolls 9 and 10 is directed' by rolls 11 and 12 into awater bath maintained in'a pan 13. Inasmuch as cellulose ber has muchgreater affinity for water y the pan '13 and `re-employed in thesolvent.

pan 8.

If^ solvents miscible with Water are employed to extract the resinousimpurities, it may be more expedient to handle the ber in the form of apulp or shredded paper suspension, in order to provide an economicalmethod of displacing and recovering the solvent. Extraction of the pulpmay be lintermediate portion to substantially only water at the otherend, is maintained in the apparatus. Water is continuously fed into oneend ofthe apparatus, and a iow of solvent. is produced from bath `tobathtoward thc other end from which water is discharged and into whichpulp to be extracted is continuously fed in countercurrent flow to thewater. A volume of solvent is continuously withdrawn from'the apparatusat the desired point to prevent the concentration of coloring impuritiesinthe solvent, and sufficient' -fresh solvent to make up losses and toreplace solvent being withdrawn is continuously introduced into theintermediate portion of the apparatus.

As shown in Figure 2, the apparatus comprises a series of sections, eachconsisting of a storage tank containing a pool of solvent and anextracting tank associatedftherewith and located thereabove. The lsovent in the successive storage tanks ows in direction opposite to theflow of the ber. `These tanks are indicated at 2l, 22, 23, 24, 25, 26,v100 27, 28, 29 land 30, in the direction of solvent flow. The solventoverflows a series of partitions 31 placed between the tanks andgradually decreasing in height from the tank 21 to the tank 30, so thatsubstantially con 10;, tinuous ow of solution from .the tank 21 to thetank 30 results. The extracting tanks are designated as 21, 22a, 23a,24, 25, 26a, 27a, 28, 29a and 30, in the direction of the ow of ber.Each treating tank is divided 110 into two compartments. First, there isa Vthickening compartment 32, in which rotatesv a straining cylinder 33,on which :ber is deposited and through which the solvent passes and isreturned by a pipe 34 to the 115 corresponding storage tank. The berdeposited on the straining cylinder is squeezed and thickened by a pressroll 35 bearing against the cylinder. The ber is removed from thecylinder ad deposited 1in an agitatl "1z0 ing compartment 32a containingthe solvent, by a scraper or doctor 36 actin against the cylinder andstationed on a partition 37 serving to divide the thickening. andagitating compartments. A supply of-solvent is main- 12u tained in eachextraction tank by withdrawing solvent from the corresponding storagetank by a pump 370, and delivering it through a pipe 38 into theagitating compartment. The ber isv vagitated in the solution 130maintained in the extracting compartment by a pair of agitators 380, andflows over a partition 39 into the next adjacent thickening compartment.There is thus'a. constant circulation of the solvent from each storagetank, through the\ agitating compartment of the extracting tank, andthence through the straining cylinder back to its storage tank. The pulpis introduced into the first extracting tank 21 through a pipe 42 andafter extraction is withdrawn at the other end of the apparatus from theextracting tank 30 through a pipe 43. The solvent is introduced into theextracting tank 25a through a pipe 45, and'water is introduced,

into the storage tank 21 through a pipe 44 and withdrawn from thestorage tank 30 through a pipe 46.

The fiber may be delivered intofthe apparatus as, say, a 10% to 12%aqueouspulp suspension. As it passes through the successive extractingtanks toward the center of the apparatus, the water associated there`.with is displaced by solvent of increasing strength, and acquires amaximum solvent concentration when 1t reaches the extractlng tank 25a,into which the solvent is introduced. On passing forwardly from the..

tank 25, the solvent associated with the fiber is displaced by solventof progressively decreasing strength, and when the fiber 1s dischargedfrom the last extracting tank 30a, thesolvent is substantially entirelydisplaced by water. Operation may be initially commenced by maintainingthe volume of solvent continuously delivered into the extracting tank25a, and the volume of water continuously introduced into the storagetank 21 substantially equal to the volume of water associated with theraw fiber. The apparatus is controlled to discharge a fiber having Y awater content equal to that of the raw fiber,

. substantially only water, therefore, being discharged through theoutlet pipe 46. After the equilibrium concentration of solvent has beenattained in the tanks, only suifcient solvent to make up for thelsolvent bled off from the storage tank 25 through a valved pipe 49 andto make up losses need be'introduced into the extracting tank 2,5, Thevolume of water introduced into the storage tank 2l is then maintainedsubstantially equal to the water content of the raw fiber as it isintroduced, and the Water discharged through the outletpipe 46, so thatthe concentration of solvent in each of the storage andr extractingtanks remains, substantially constant during the continuous operation ofthe apparatus. the pipe 49 is regulated to provide for the withdrawal ofsuiicient solventA to prevent accumulation of extracted matter in theapparatus. This bled-off solvent may be evapresinous from the fiber.

The How. bled( off through resinous impurities contained therein.

orated for the recovery of its valuable solvent content.

The process of extraction may be considered as comprising two steps,during both of which steps an extraction of material from T the fiber bythe solvent is effected. First, the gradual displacement of the watercontent of the fiber by solvent occurs, and then the gradualdisplacement of the solvent by water. Consequently, substantially allthe solvent except that drawn 0H through the bleed pipe 49 is maintainedwithin vthe apparatus, substantially only water accompanying theextracted fiber discharged through the pipe 43 at one end of theapparatus, and substantially only 'water being discharged through theoutlet pipe 46 at the opposite end thereof. If the treatment iscarriedout at an elevated temperature, as by introducing low pressure steaminto the central pool maintained in the 1 storage tank 26, the heatcontent, except for that of the bleed solution and that lost due to llevaporation of solvent, is maintained within the apparatus. Thecounter-current process thus described may be approximated in.

simpler apparatus through the use of tanks or centrifuges piped to allowthe countercurrent displacement of water or of solvent in the stoc Wherean inert solvent is employed,it may be advantageous to add otherchemicals to efi'ect a removal `of impurities otherwthan Thus, a certainamount of chlorine may be added to a solvent such as carbontetrachloride to remove residy ual lignin. To a solvent such as alcohol;for

example,`a small quantity of caustic soda may be added to remove betaand gamma celluloses and other non-alpha cellulose components carried bythe fiber. Alone or in addition to the caustic soda, soap may be added.Soap aids in the removal of resinous impurities, as

it tends to disperse them and also has a detergent efl'ect upon speckspresent inthe fiber.

A process such as described makes possible the use of ber quite high inresinous impurities, for such fiber may be deresinified -to a pointwhere it is quite suitable for the manufacture of high grade` papers andderivatives. Our process, therefore, permits the use of highly resinouswoods in the production of pulp, for resinous impurities surviving thefiber-liberating process or subsequent chemgi:A cal treatments may besatisfactorily removed.

Having thus described certain embodiments of this invention, it shouldbe evident to those skilled in the art that arious changes andmodifications might bemade therein without departing from the spirit orscope of invention as defined by the appended claims.

We claim 1. A process which comprises treating oellulose` fiber freedfrom encrusting material with organic solvents to effect a removal of 2.A process which comprises tileating cellulose liber with a plurality ofdifferent organic solvents capable of extracting diferent resinousimpurities lcontained therein.

. 8. A process which comprises treating ce1- lulose fiber freed fromencrusting material with an organic solvent capable of eii'ecting aremoval of resinous impurities and cont-aining a chemical capable ofreacting with and removing other non-alpha cellulose componentsin saidfiber.

4. A process Which comprises treating cellulose fiber With organicsolvents to effect the y extraction of resinous impurities carried ftherein, displacing the solvent With Water,` and recovering thedisplaced solvent for the treatment of other fiber.

5. A rprocess which comprises passing a sheet of cellulose fiber`througha Water-immiscible solvent bath to eiect the extraction of resinousimpurities containedtherein, passing the sheet through a Water bath,thus displacing the solvent in said sheet by Water and forming a layerof solvent in said Water bath,`

and removing and recovering said solvent for use in said solvent bath.

6. A rocess which comprises treating cellulose ber with a succession ofdifferent organic solvents, each capable of extract- 7. A process whichcomprises treating cell lulose ber with alcohol and then with carbontetrachloride. I

8. A process which comprises first passing a sheet of cellulose fiberthrough a Watermiscible organic solvent and then through aWater-immiscible organic solvent,` passing the sheet through a Waterbath thus displacing the Water-immiscible solvent in said sheet byWater, and removing and recovering said displaced solvent.

9. A process which comprises first passing a sheet of lcellulose iberthrough alcohol and then through carbon tetrachloride.

10. A process which comprises first passing a sheet of cellulose fiberthrough alcohol and then through carbon tetrachloride, passing the sheetthrough a Water bath thus displacing the carbon tetrachloride in saidsheet by Water and forming a layer of the same at the bottom of saidbath, and removing and recovering the displaced carbon tetrachloride.

11. A process `Which comprises treating cellulose fiber with organicsolvents to eect a removal of resinous impurities, and converting thecellulose thus purified into cellulose derivatives.

12. A process which comprises treating cellulose fiber with an organicsolvent capable of effecting a removal of resinous impurities containedtherein, and then displacing the solvent With Water.

13. `A process Which comprises treating cellulose ber with aWater-immiscible soll vent `capable ofeii'ecting aremoval of resinousimpurities contained therein, and then treating the fiber in a Waterbath, thus dlsplacing its solvent content with Water and signatures.

MILTON O. SCHUR.

ROYAL H. RASCH.

